Plasma-assisted dry processes are used in widespread technologies such as semiconductor manufacturing apparatuses, surface hardening of metal components, surface activation of plastic components, and chemical-free sterilization. For example, various plasma processings such as ashing, dry etching, thin film deposition, and surface modification are used in manufacturing semiconductor devices and liquid crystal displays. Plasma-assisted dry processes are low-cost and high-speed, and also have an advantage that environmental pollution can be reduced because no chemicals are used.
A typical apparatus for performing such plasma processing is a plasma processing apparatus of the “microwave excitation type” where a plasma is excited by a microwave having a frequency of 100 MHz to several 10 GHz. The plasma source of the microwave excitation type has a lower plasma potential than high-frequency plasma sources and the like, and hence are widely used for damage-free resist ashing and voltage-biased anisotropic etching.
The area of semiconductor wafers and liquid crystal display glass substrates to be processed is increasing year by year. Hence plasma processing therefor requires a plasma generating apparatus capable of generating a plasma dense and uniform over a large area.
In response to such requirement, one of the inventors disclosed a plasma processing apparatus where a microwave guided through a rectangular waveguide is introduced into an annular space through a coaxial line and introduced into a chamber through a plurality of arc-shaped slits (Patent Document 1),    Patent Document 1: JP-A 2003-124193 (Kokai)
However, workpieces subjected to plasma processing are growing larger and larger in size, and there is a demand for a plasma generating apparatus capable of stably generating a plasma uniform over a large area. Furthermore, during actual plasma processing, the conditions of plasma processing may be often changed variously depending on the type and number of workpieces. Hence it is desirable that a uniform plasma can be stably generated over a wide range of conditions.
The invention has been made on the basis of recognition of these problems. An object of the invention is to provide a plasma generating apparatus capable of stably forming a plasma having a uniform distribution over a large area and a plasma processing apparatus equipped therewith.